This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present technological advancement. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present technological advancement. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Prior systems, methods and devices have been developed to separate unwanted constituents of a gaseous mixture using a pressure swing adsorption (PSA) process. This process generally comprises a feed step and a regeneration step. The feed step being one during which a feed gas, which is a mixture of at least two constituents, is passed over adsorptive media bed(s) to remove a more readily adsorbed constituent of the mixture from the remaining constituents that are less readily adsorbed. During regeneration, the more readily adsorbed constituent is removed from the bed(s) generally by pressure reduction, gas sweeping, purging or a combination of these. Generally, the feed step takes place at a substantially higher pressure than the regeneration step, hence the description of “pressure swing adsorption.”
The adsorptive media is arranged in a bed of some architecture, such as a packed bed, coated ceramic monolith, coated foil, etc. and has a normal direction of flow through the bed from the feed side to the product side of the bed. The device comprises ports that may be alternately in communication with the bed or in communication with the bed in combinations. The ports comprise at least one feed port, at least one product port, at least one blow down port, at least one purge supply port and at least one purge vent port.
During the feed step, the feed port and the product port are in communication with the bed. The pressurized gaseous mixture containing one or more unwanted constituents flows from the feed port, through the bed in the normal direction of flow and passes over an adsorptive media to produce a pressurized product stream with a reduced amount of the unwanted constituents and this pressurized product stream flows out of the product port; the unwanted constituents being more readily adsorbed onto the adsorptive media than the other constituents.
In order to regenerate the adsorptive media, the unwanted constituents may be removed by a pressure swing process comprising the following steps: 1) stop flow from the feed port and out of the product port; 2) depressurize the bed in one or more steps to a lower pressure by flowing the residual gaseous mixture contained within the device to the blow down port that is then in communication with the bed and with flow in the normal direction across the bed such that the residual gaseous mixture leaving the blow down port has a reduced amount of the unwanted constituents to form a lean residual gas; 3) stop flow from the blow down port by stopping communication between the blow down port and the bed; 4) by some means store the lean residual gas for use in step (5) or as an alternative, this lean residual gas may be used concurrently without storage in another similar device; 5) open communication between the bed and the purge supply and the purge vent ports, the purge supply and purge vent ports being located such that the lean residual gas that flows into the device through the purge supply port passes through the bed in the anti-normal direction and leaves the device through the purge vent port as a rich residual gas.
As is normal with a pressure swing process, the lean residual gas, being at a lower pressure and possibly also a higher temperature than the feed gas, has a greater capacity to capture and remove the unwanted constituents from the adsorptive media to create the rich residual gas. The rich residual gas may be further conditioned and recycled to the feed gas, used in another process or disposed.
U.S. Pat. No. 4,452,612 (the entirety of which is hereby incorporated by reference), which will be referred to as Mattia, and U.S. Pat. No. RE40,006 E (a reissue of U.S. Pat. No. 6,063,161, the entirety of which is hereby incorporated by reference), which will be referred to as Keefer, describe the art of pressure swing adsorption using a plurality of adsorptive beds with a rotary valve arrangement to manage the feed and regeneration steps. Mattia describes the basic principles for pressure swing adsorption using rotary valves in which a plurality of adsorptive beds successively pass by several ports separated by baffles and seals to effect the feed, depressurization, desorption and re-pressurization steps of the process. Mattia describes the use of a plurality of beds that rotate at the same speed such that for example, depressurization of one bed may be used to purge and regenerate and the re-pressurize other beds. In this manner, the beds are interconnected to reduce the need for external compression and improve the efficiency of the pressure swing adsorption process.
Keefer builds on Mattia to further teach a method to control the pressure swing adsorption process in which pressure or flow control devices, such as control valves, orifices and the like, are included within the interconnecting lines between the beds. In this manner, the effective flow coefficient (Cv) of these interconnections may be adjusted to alter the time to complete a purge, depressurization, re-pressurization or similar sub-steps of the regeneration step. This ability to control the Cvs of these interconnections may be useful to adapt the pressure swing adsorption process to varying feed compositions, flow rates, turndown or other process variables.